Electrical heater resistance element



LlUlhHllIl-l\ R. w. REYNOLDS. ELECTRICAL HEATER RESISTANCE ELEMENT.

APPLICATION FILED FEB- 18. I921.

1,422, 130, Patented July 11, 1922.

' detachably in a heater device such as a means of a brush, and the dried in a water bath and preferably stoved 95 to the surface to be heated so lon resistance elements of the film type, that is insulating surface provides a -of an electrical current passing through it. add thereto 6 UNITED STATES PATENT OFFICE;

ROBERT woouuner: REYNOLDS, or nannmenuasr, NEAR sxnmm-mzw scum; warns, aus'rmm.

ELECTiICAL HEATER RESISTANCE ELEMENT.

1,422,130. Specification of Letters Pa tent.

Application filed February 18, 1921. Serial No. 446,079.

T all h jt a cmwem; In carrying out the invention, powdered Be it known t lat I, Ro mn'r WOOLRIDGE ra hlte is incorporated with a mmor pro- REYNOLDS, a subject of the King of Great portlon of sodium silicate@ tassium sili- Britain and Ireland, residing at 61 Roslyn cate in a Slllclc veh cle wl'iicfi l'ias 5e en Street, Darlinghurst, near Sydney, New 0 emicall reel 1ta e rom an a ueous. South \Vales, Australia, have invented new So u mu 0 so lum s1 lcae or oasslum s1 1- and useful Improvements in Electrical cate to form a paint-ilk mixture which is Heater Resistance Elements, of which the ada ate 0 a o ication in means 0 a following is a specification. rush to form a uc m wlin ap-- This invention relates to electrical heater plied to and dried and set .on an electrically conductive to say, the type in which a film of substance path having appropriate resistance for the having low electrical conductivity, as conproduction of heatin efi'ects when it is tradistinguished from a resistance constructtraversed by an electrical current. ed of convolutions of a thin metallic wire In practice I take an aqueous solution of or tape. is raised in temperature by means commercial sodium silicate and gradually su ate, c on e, or other solu- The invention consists in an electrical reble salt of umlnlum, in a ueous solution. sistance element constituted of a film of A white elatlnous reel 1 a e us progreater or less thickness and superficial diduced. l he addltlon of the aluminium salt mensions, composed of powdered ra bite is continued only as long as precipitation and chemically precipitated alumip runrs j continues, and then the precipitate is perca te or certain other chemically precipitated mitted to settle for ten to fifteen minutes, more or less. After removal of the bulk of silicates.

Resistance films according to the present the supernatant liquor by siphoning, -or invention are applied as a paint which is otherwlse, the precipitate is washed in water adhesive to a support surface. Usually they. several times-usually five times-with the are applied over a protective surfacing of object of removing water-soluble salts. At

Patented July 1.1, 1922.

electrically insulating enamel on a metallic the end of each such washing, the precipitate sheet-or plate, such for instance as the botis allowed to settle and the waste water retom of a 'Water kettle. But they may be moved by siphoning or decanting, cam beapplied to a strip of mica or like electriing taken to revent loss of precipitate. To cally non-conductive and heat tolerant the final was ed precipitate, very fine fiou material, and protected against short cir- T cuiting by an appropriate insulatin ing or jacket to form a self-containe unit ra e y mixing. The mixture so obtained, which may be fixed either permanently or is immediately usable.

It is applied b applied film is aii kettle or water boiler.-

To minimize heat losses, it is usually desirable to apply the resistance film directly before current is passed through it.

as such For the making of heater resistances for glaze use on circuits carrying an electrical presto set it hard and to remove free moisture surface is protected bya fire ename led or like effective electrical insulator Skll'l to sure of about 240 volts, prevent short-c-ircuiting of the current there- I ture is obtained by takin through. Films manufactured in the mancommercial water lass ner hereinafter described are homogeneous 35% of sodium SlllCflEl,

about 8 oz. of containing about diluting and thorand possess the property of setting evenly oughly mixing it with 8 oz. water, comon t e adhering tenaciously and permapletely precipitating the solution with aguenently to smooth surfaces, such as the surous solution of alum' 1 hate, allowlng faces of enamel or mica; under conditions of the precipitate to settle, decanting or siphonuse in which they suffer repeated heating ing ofi' the supernatant liquor repeatedly and coolingythey do not granulate, craze, or washing the precipitate with fresh water, scale, and they do not substantially change and after decantin use. itate'and thoroughly intermixing therewith ra bite and a minor proportion of so mm 90 coverslllcate are added and thoroughly incorpo a satisfactory mix- 1.00

or siphoning off the -in specific electrical resistance after initial final wash water, ad ing to the clean precip- 4 oz. of fine flour a bite and one fluid ounce of commercial wafir lass. The product thus obtained is su1 a e or immediate application as a paint, to form a film resistance.

It has been determined that an effective method of applyinfinthis pain to form a remains practical] cased in strung to this invention. 45

heater resistance fi is to apply it in two or more superposed coats, drying of! each coat before a p ying the next one, and crossing the brus lines in the successive coats. A one-thickness coat of adequate thickness is liable to be less regular than a multiplethickness coat.

The conductivity of the film augments during its first electrical heating to about 25% over its conductivity when the first passing of current occurs; thereafter it constant. Experience shows that it is deslrable to make the length of the film stri not less than five inches, though quite e ective results may be got with films of shorter length. No difiicu ty is found in determining'with approximate accuracy the current capacity1 of a paintedon film of this product wit a current of known constants. ness of the film will de nd upon the fluidity of the material, which naturally will vary to some extent accordin to the proportion of wash water left with t e precipitate after the final washing, a little experience must be gained by practical test to enable a workman, however skilled, to determine with ipproximate accuracy the dimensions and coat' thickness of the film required to roduce a certain desired heatin effect. ontact is made with the thickene end portions by a strip of wire gauze fixed thereon, a current conducting terminal being attached to the gauze.

The accom anying drawing shows m spective section a heater element acco mg The element is shown a plied to a metal plate over fire enamel glhze. The thicknesses of the plate, the

laze, the film, and the gauze connector are siown in greatly exaggerated proportion to facilitate explanation.

A is a metal plate to which heat is to be -a plied; B fire enamel glaze thereon; C fi of resistance material painted over the glaze B; D strips of wire gauze set on the ends of the film C; E painted-on edging of resistance material securing the gauze strips D to the film C; F wire connectors soldered or otherwise permanently secured to the middle part of the gauze strips D to provide a permanent electrical connection. The wires F are led to pin lu or other sultable electrical couplm evices, and may be enad insulators G.

The gauze connector stri D are set in position after the film C 1s ry and they are Inasmuch as the thick-' on a strip Eofihe resistance material, to bind the edges to the film and provide a good electrical connection. The middle portions 'of the stri s B should not be attached to the film C. by painting the edging material C all over .the strips, the stri s are liable to eel off.

As a rou h gui e to indicate t e dimensions of a lm required to obtain effective results on a water kettle bottom, I say that test films five inches long used in a 240 volt circuit safely carry one ampere of current for every inch in width, and that the current flux can be increased by one half ampere per inch width for each additional inch of length beyond five inches; thus a film strip seven inches long by two inches in width will effectively carry a current of 4 amperes. It is found undesirable to increase the current density substantially beyond the ranges indicated by these figures.

' I have also experimentally established the fact that when an aqueous solution of sodium silicate or potassium silicate is precipitated by a soluble salt of an alkaline earth metal. orbg'asou esato zlncoriron apr uc is o tame w 1c can "in the same .manner (thou h with inferior results) as port, terminal wiring attachments mounted on said support, a painted on and dried out film surface containing 'awater-washed chemicall precipitated silicic vehicle, and powdere graphite incorporated in said silicic vehic e.

2. An electrical heater resistance element com rising a conducting base, an electricity insu ating surface, a painted on and dried out film containing a water-washed chemi cally precipitated silicic vehicle, powdered graphite and alkali silicate, and metallic terminal attachments contactin with said film surface at oppositeedges t ereof.

3. In an electrical heater resistance element as set forth in claim 2 a film surface comprising a water-washed chemically precipitated aluminous silicic vehicle, powdered graphite and alkali silicate.

4. In an electrical heater resistance element as set forth in claim 2 a film surface f they are at ached to it as comprising a water-washed chemically pre- In testimony whereof I have signed my name to this specification.

ROBERT .WOOLRIDGE REYNOLDS. 

